Reducing bath for color photography and process of using the same



silver salts.

Patented Feb. lb, i943 REDUCHNG BATH FOR WLOR PHOTOGRA- PHY AND PRUCES'S01F USWG THE SAW Emery Mescliter, Militown, N. 3., assignor, by to E. i.du Pont de mcsne assignments, Nemours & Company, poration oil DelawareWilmington, melt, a cor- No Drawing. Application September 19, 1939,Serial No. 295,685

5 Claims. (0C1. 95-88) This invention relates to photography. Moreparticularly it relates to reducing compositions for reducing silversalts to metallic silver. Still more particularly it relates to dyegenerating reducing compositions which are useful in color photography.Still more particularly it relates to aqueous reducing baths containingan aromatic polyamino developing agent having at least one unsubstitutedamino group and a nitrogenous base free from neative groups and hydroxylgroups attached to carbon atoms. Still more particularly it relates toaqueous reducing baths containing an aromatic polyamino developing agenthaving at least one unsubstituted amino group and a nitrogenous basefree from negative groups and hydroxyl groups attached to carbon,capable of energizing said developing agent so that it no longer actspreferentially. on exposed The invention also relates to processes ofreducing photographic images utilizing the herein-described reducingbaths.

This invention has for an object the preparation of active reducingbaths from photographic developing agents. A further object is toproduce a reducing composition which will reduce metallic saltsespecially unexposed silver salts of the type used in photographicemulsions to metallic silver. A still further object is to provide anaqueous reducing bath which does not distinguish in its reducing actionbetween unexposed and'exposed silver salts in a photographic emulsion. Astill further object is to provide a. re-

ducing composition which may be used in a reversal process involving noreexposure to light.

Another object is to provide a reducing bath which may be used forsimultaneously reducing silver salts and forming. colored dyes in situtherewith. Another object is to provide an aqueous reducing compositionwhich will increase the effective speed of photographic emulsions informing colored images, especially reverse images. Other objectsinclude'the production of reducing compositions which when used inprocesses of color-photography result in color photographs of improvedquality, saturation of individual color components and brilliancy ofindividual and combined dye images. A further object is to providereducing baths which are of general utility in the dyeing arts.

The above and other objects are accomplished by the following inventionwhich comprises a composition containing an aromatic polyaminodeveloping agent containing at least one unsubstituted amino group and anitrogenous basefree from negativegroups and hydroxyl groups attached tocarbon.

In a more limited sense the invention comprises the preparation and useof an aqueous bath containing an aromatic polyamino developing agentcontaining at least one unsubstituted amino group and a nitrogenous basefree from negative and hydroxyl groups attached to carbon, capable ofenergizing said developing agent so that it no longer actspreferentially on exposed silver salts.

In a still more limited sense the invention comprises an aqueousreducing bath containing an arylene diamino photographic developingagent and a water-soluble nitrogenous basefree from negative groups andhydroxyl attached to carbon, capable of energizing said developing agentso that it no longer distinguishes between ex- 'posed and unexposedsilver halides in its reducing action.

The energizing agents which change aromatic polyamino developing agentscontaining at least one unsubstituted amino group and-especially thosefree from negative and hydroxyl groups do not fall into any one specificclass of bases but fall within numerous classes. The operativenitrogenous bases as previously stated are free from negative groupssuch as halogen atoms, e. g. Cl, Br: nitro, $03M, COOM wherein M is H,or a metal, and hydroxyl groups, attached to carbon. The bases which arewater soluble or can be readily dispersed in aqueous systems are mosteffective. Bases which do not have the above constitution, for example,the alkylol amines, e. g. mono-, di and tri-ethanol amines; do notfunction in the reducing solutions of the present invention.-

An important class of nitrogenous bases which are organic amines may berepresented by the general formula:

R'\-N K wherein each R, R and B" may be hydrogen, allgvL-cycloalkyl,aryl, aralkyl, or wherein two R's may represent a divalent polymethylene.dodecyl, tetradecyl, octadecyl.

hydrocarbon or R, R and R" together may represent a trivalenthydrocarbon radical such as a polymethanyl radical which, with thenitrogen atom, forms an N -heterocyclic nucleus.

Another important class of compounds which are quaternary ammonium basesmay be represented by the general formula:

N-OH

wherein each R1, R2, R3 and R4 may be hydrogen, alkyl, cycloalkyl, aryl,aralkyl, and further characterized in that the methylene groups may besubstituted by alkyl, cycloalkyl, aryl and aralkyl groups and at leastone of the methylene groups may be substituted by amino groups, and n is1 to 8.

As examples of suitable alkyl groups which may be present in each of theabove formulae mention is made of methyl, ethyl, propyl, isopropyl,n-butyl, tertiary butyl, pentyl, isopentyl, octyl,

Suitable cycloalkyl radicals include cyclobutyl, cyclopentyl, andcycohexyl. Suitable aryl radicals include phenyl, tolyl, a-naphthyl,p-naphthyl, etc. Among the useful aralkyl radicals may he mentionedbenzyl, z-methyl benzyl, naphthyl methyl, etc.

The objects are attained in a refinement of the invention by thepreparation of reducing compositions, particularly aqueous .bathscontaining an N-dialkyl phenylene diamine of the general formula:

or a water soluble salt thereof, wherein R and R are the same ordiflferent lower alkyl radicals, e. g. methyl and ethyl; and anitrogenousbase free from negative groups and hydroxyl groups andfalling within one of the Formulae 1, 2, and 3.

It has been found according to this invention that the arylene dlaminocompounds, particularly those of the type set forth in Formula 4 aboveand their water soluble salts become very active reducing agents whenthey are admixed with nitrogenous bases of the above type especiallythose falling within one of the Formulae 1, 2 and 3. This discovery isof considerable importance in that it enables the relatively weakreducing agents, namely, the arylene diaminocompounds,tobeusedinagreatmanyarts, wherein only powerful reducingagents have heretofore been used without the attendant disadvantages ofthe last mentioned agents.

In an important embodiment of the invention the reducing compositionscontain in addition to the aromatic polyamino photographic developingagent and nitrogenous base which energizes its reducing powers, a colorformer which will couple with the products formed ,duringthe reducingaction to form a dyestuif of the indophenol or azomethine type.

The N-dialkyl p-phenylene diamines, which are rather weak photographicdeveloping agents, when used in conjunction with basicagents hereinspecified become highly energized and are no longer selective in theirreducing action. They lose their ability to differentiate betweenexposed and unexposed silver halides 'in their reducing action and nolonger act like photographic developing agents. On the contrary, theybecome overall reducing agents, acting similarly to sodium hydrosulfite,sodium stannite, etc. in regard to silver salt reduction.

In addition to causing weak photographic developing agents, e. g.1:4-diaminob =:nzene, 1:4- diamino-naphthalene,- p-aminodiethyl aniline,p-aminodiethyltoluidine, etc. to become overall silver halide reducingagents, the addition of the nitrogenous bases free from negative groupsand hydroxyl groups vastly increases the dye-forming characteristics ofthese dye-generating baths which is surprising and unexpected. Thus, ithas been found that with a given silver density produced by theconventional type of color-forming developer containing sodium orpotassium carbonate as the alkali, a much greater density of dye imageis produced with the same silver density by these dye-generatingreducing baths. Furthermore, this occurs at the same pH condition of thebath as that containing alkaline carbonates. At least 40%, and sometimesas much as 70% greater dye density for the same amount .of reducedsilver halides is produced by these dye-generating reducers comparedwith ordinary carbonate containing color-developers. In addition, therate of increase in dye-density with alkaline carbonate, or even causticalkali, containing color-developers rapidly diminishes after 5-8 minutesdeveloping time. With the dye-generating reducers of the presentinvention, on the other hand, the increase in dye-density continues evenafter 15 minutes developing time. The specific types of nitrogen basesdescribed above result in three major unexpected and surprising resultswhen used with arylene-diamine developing agents in the presence ofquinoneimine, azomethine and azo dye-forming components:

1. Weak photographic developing agents become energetic over-allreducers for silver halides and are no longer photographer developers.

2. For the same amount of silver produced. these dye-generating reducersyield greater amounts of dye.

3. The formation of "ye with these dyegenerating reducers continues longafter the usual color-developers have ceased to produce greater dyedensity.

The present application is limited to the reducing compositionsincluding those containing color-formers. Processes of producing coloredimages involving the use of these reducing bath: particularly reversalprocesses and processes involving the use of multi-layer film containingcolor formers, are claimed in a copending application Serial No. 295,686of E. Meschter. en-

titled Color Photography. filed upon an even datr herewith.

The present invention will be further illus trated but is not intendedto be limited by the following examples:

Example I An aqueous bath of the following composition:

p-no-N-dlethylaniline grams 2 Ammonium hydroxide, cone cc 25 Sodiumsulfite, anhy grams 2 Water to liter 1 was prepared by adding theammonia to a solution of the sodium sulfite and then adding thedeveloping agent. Water was then added to make one liter.

An exposed negative film was developed in a metolhydroquinone developerand without fixing, the silver image was removed in a sulfuricacidpotassium dichromate, washed, then treated without re-exposure inthe above reducing bath. h reversed image of good quality was readilyformed.

Example II aqueous bath of the following composition: odiethylanilinegrams 2 Hexamethyienediamine (54% solution) cc 15 Sodium sulfite, anhygrams 3 Wate to liter" 1 was prepared after the manner set forth inExample I. It had excellent reducing properties for silver halides.

Other reducing baths which have similar properties are set forth in thefollowing examples:-

2 -Amino-5-diethylamino-toluene grams 5 Tethyl-benzyl-ammonium hydroxidecc 20 Sodium sulfite, anhyl grams" 5 Water tn liter 1 Example VII Iizt-Diaminodiphenylamine "grams-.. 4 Hexamethylenediamine do Sodiumsulfite, anhy ..-do 2 ater to 111m 1 Example VIII l :d-Diaminonaphthalengrams 3 Dimethylcyclohexylamine cc 30 Sodium sulfite, anhy grams 3 Waterin lif.a=r 1 Example IX i-Diethylamino-l-naphthylamine grams 5 Example Xp-Aminodibutylaniline grams 3 Hexamethylenediamine do Sodium sulfite,anhy -do 2 5 Water to liter 1 Example XI p-Aminodiethylaniline grams 3Trimethyl-benzyl-ammonium hydroxide cc 0 Sodium sulfite, anhy grams 3Water in liter" 1 When the developing agent is used in the base form itshould be incorporated in the solution after the sulfite and nitrogenousbase have been added. In the salt form the sulfite is added first, thenthe developing agent, then the nitrogenous base.

Example XII 20 A dye forming reducing bath of the following composition:

a-chlor-ethyl-aceto-acetate grams 2 p-Amino-N-diethylaniline do 2 25Ammonium hydroxide (conc.) ..-cc 25 Sodium sulfite, anhy grams 2 Waterto liter 1 was prepared by the above manner by dissolving thechlorethylacetoacetate in acetone and adding it and the otheringredients to water and bringing the solution up to 1 liter.

A film which had been exposed and developed in a metol-hydroquinonedeveloper and the silver images removed by bleaching was treated in theabove solution, whereby a reversed yellowdye and silver images wereformed. The silver image was removed in the usual manner, leaving ayellow image. p

Example XIII A dye forming reducing bath of the following composition:

Thioindoxyl-carboxylic acid .grams 2 p-Amino N-diethylaniline do- 3fi-Dimethylaminoethylamine cc 20 Sodium sulfite, anhy "grams--. 3 Waterto liter 1 is prepared by adding the thio-indoxyl-carboxylic' aciddissolved in 20 ocs. of acetone and the other ingredients to water andbringing the solution to a volume of one liter.

An unexposed reversed silver salt image, when treated in the abovesolution, forms a magenta dye image in situ with metallic silver. Uponremoval of the silver a magenta image ofgood strength and clarity isobtained. Example XIV A dye forming reducing bath of the following 0composition:

Trichlornaphthol grams 2 2-amin0-5-diethylamino-toluene d0 5Hexamethylenediamine -do 10 Sodium sulfite, anhy --do- 5 Water to. liter1 is prepared by dissolving the trichlornaphthol in acetone and addingit and the other ingredients to water and bringing the solution to avolume of one liter.

An unexposed reversed silver salt image when treated in the solutionforms a blue-green image lB-dimethylaminoethylamine cc- 20 in situ withmetallic silver. I Upon removal of the sodium sulfite, anhy r ms" 5silver a blue-green image of excellent density an 1mer clarity wasobtained,

In place of the aromatic polyamino developing agents free from nuclearhydroxyl groups set forth in the above examples, may be substituted inwhole or in part one or more other specific compounds. Suitableadditional compounds ofthis type. which are known photographicdeveloping agents include:

1 :4-diaminobenzene and their water soluble salts, e. g. chloride,sulfate, acetate, oxalate, etc.

Similarly, other basic compounds which cause the above developing agentsto become overall reducing agents may be substituted in whole or in partfor the specific bases set forth above. Thus, one or more of thefollowing may be used: Lower alkylamines such as mono-, diand trimethyl,ethyl, n-propyl, n-butyl, etc. amines, which contain no negative groupsand hydroxyl groups in the hydrocarbon radicals; straight and branchedchain alkyl monoand poly-amines free from nuclear negative and hydroxygroups, e. g. ethylenediamine, hexamethylene diamine, triaminopropane,p-dimethylamino ethylamine, n-propylamyl hexylamine, tri-n-amylamine,di-

iso-amylamine, cyclic and heterocyclic amines,

e. g. piperidine, N-methylpiperidine, N-ethyl piperidine, piperazine,N-dimethylcyclohexylamine, N-ethyl-N-methyl cyclohexylamine,n-octyl-pyridinium hydroxide; quaternary N-hydroxides free from nuclearsubstituted negative groups and hydroxyl groups, e. g.:

Trimethylbenzylammonium hydroxide Tetramethylammonium hydroxide nDodecyldimethylcycloh'exylammonium droxide n-Dodecyltrimethylammoniumhydroxide n-Octadecylbenzyldimethylammonium hydroxiden-Dodecylphenyldimethylammonium hydroxide The nitrogenous bases freefrom negative groups and hydroxyl groups which may be used in practicingthis invention are further characterized in that they have anassociation exponent .(pkab) of about 5.00 to about 12.00 and preferablyfrom 9.0 to about 11.40.

The proportions of the components of the reducing solutions may bevaried considerably. For instance, the amount of arylene-diaminodeveloping iagent may vary from 2 to 12 grams per liter with goodresults. The amount of alkali metal or ammonium sulfite may vary from 15to 25 grams per liter of solution. The amount .of weak alkali, e. g.sodium carbonate may vary from to 30 grams per liter. With regard to thenitrogenous base free from negative groups and hydroxyl groups, it mayvary from 8 to 30 grams or ccs. per liter of solution.

Likewise, other color forming compounds may be substituted for thespecific ones set forth in the above examples. As examples ofrepresentative suitable color-formers which are soluble or readilydispersible in the reducing solutions arediacylacetamino-aryl-bis-thiazoles of U. S. Patent 2,140,540, of whichdifuroylacetamino-1,2,4,5- benzo-bis-thiazole is preferred, theacylacetarylides of U. S. Patent 2,108,602, acetyl acetone, benzoylacetone, B-naphthoyl acetone, acetoacetic esters,ethyl-a-chloroacetoacetate, ethyl-'y-chloroacetoacetate, ethyl malonate,ethyl-p-nitrophenyl-acetate, ethyl acetopropionate, ethyl acetonedicarboxylate, furoylacetic ester, the acylacetamino phenyl morpholinesof U. S. Patent 1,133,937, etc.

Suitable magenta color-formers include nitriles, e. g. p-nitrobenzylcyanide, o-nitrobenzylcyanide, p-toluyl-acetonitrile,w-cyanoacetyl-dibenzfuran, w-cyano-acetyl-acenaphthene,l-w-cyanoacetylcoumarone, cyanoacetyD-benzene, acyl nitriles, e. g.cyanacetophenone, methoxy-a-naphthoylaceto-nitrile, cyanacetanilides, e.g. l-cyanacetaminohenzthiazole, etc., pyrazolones, e. g.

Suitable blue-green color formers include phenols, e. g. ortho andmeta-chlorophenol, o-bromophenol, o-iodophenol; naphthols, e. g.2,3,4-trichlornaphthols, 2,6-dibromo-1,5-dihydroxy naphthalene, etc.Other color-formers will be apparent to those skilled in the art.

The energetic dye-generating properties of the reducers described abovemakes their particularly useful as intensifiers for silver images of toolow opacity to make them of satisfactory printing density. Thisembodiment of the invention is illustrated in the following example:

Example XV A low opacity silver image is bleached to a reducible silversalt form by a chromic acid and sodium chloride or bromide bleach bathor an alkaline-ferrocyanide bleach. The washed film is treated with adye-generating reducing bath of the above type which yields a neutralblack or grey image. If the intensified image is to be used for printingonto blue-sensitive emulsions a yellow-orange-to-red color-former can beemployed.

Intensification processes employing colorforming developers aredescribed in Fischer U. S. Patent 1,079,756 but the process describedabove constitutes a distinct improvement over the known procedures. Amajor advantage resides in the substantial increase in image opacityobtained hereby. In addition, the tonal graduations of the image asintensified by the present method do not depart as much from theoriginal tonal scale as by the prior art procedures exemplified in theFischer patent.

It is to be understood however, that the dyeforming reducing bathshereof are not limited to photographic uses although such uses are ofmajor importance. On the contrary, they are of considerable utility inthe textile and related industries. The production of dye textilematerials from natural, chemically modified, artificial and syntheticfibers is facilitated by employing reducing baths as described above.The treatment of cellulose derivatives, for instance, by the use of suchbaths, is of considerable importance. The dyeing of such materials willbe illustrated by the following example:

Example XVI Equimolecular proportions of paminodi methylaniline andl-naphthol are dissolved in water containing 50 parts per liter oftrimethylbenzyl ammonium hydroxide. The naphthoquinoneimide is formed byadding 2 parts of sodium perborate, heating the solution at about 30 C.for 15 minutes with vigorous stirring and then cooling. One part of thenaphthoquinoneimide is made into a paste by trituration with 1 to 1.5parts of sulfite waste liquor of 30 to 40% strength. To this paste isadded 2000 parts of warm water and 100 parts of acetate silk areintroduced and worked for hour while maintaining the temperature of thedye bath at 60 C. The material is then rinsed anddried. It is found thatthe depth of color is much greater and the color purity vastly improvedby this method over the usual indophenol dyeing methods. The presence ofthe coupling energizer serving here also to aid in the dye penetration.

In place of the specific color-formers and arylene diamino compounds maybe substituted others as described above. Likewise, other nitrogenousbases and other textile materials may be substituted. In a like manner,other oxidizing agentsmay be substituted for the sodium perborate.Suitable agents include hydrogen peroxide, persulfates, percarbonates,alkali metal peroxides, per-organic acids, e. g. per acetates, perpropionates, etc.

An important advantage of the present invention residues in the factthat the readily available weak arylene diamino types of developingagents may readily be converted into powerful reducing agents in asimple manner and with the aid of inexpensive and readily availableadditional agents.

A further advantage resides in the fact that a weak developing agent ofthe arylene diamine type becomes readily converted into an excellentcolor developing agent producing a much greater dye density for the sameamount of reduced silver by the addition of inexpensive and readilyavailable photographic materials. Still other advantages will beapparent to those skilled in the arts of this invention.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodiments hereofexcept as defined in the appended claims.

I claim:

1. An aqueous photographic reducing bath containing as the sole type ofreducing agent at least one photographic developing agent taken from thegroup consisting of compounds of the generalformula:

wherein R and R'are members of the group consisting of hydrogen andalkyl radicals of 1 to 4 carbon atoms and the water soluble saltsthereof and an amount of an aliphatic amine of 1 to 6 carbon atoms freefrom negative groups and hydroxyl groups. attached to carbon sumcient tochange the characteristics of the solution so that it no longerdistinguishes between exposed and unexposed silver salts, said amountbeing within the range from 8 cos. to 30 grams per liter of solution.

2. An aqueous photographic reducing bath comprising as the sole type ofreducing agent at least one photographic developing agent taken from thegroup consisting of compounds of the general formula:

wherein R and R are hydrogen or an alkyl radical of 1 to 4 carbon atoms,and the water soluble salts thereof, and an aliphatic amine of 1 to 6carbon atoms free from negative groups and hydroxyl groups attached tocarbon in an amount sufficient to change the characteristics of thesolution so that it no longer distinguishes between exposed andunexposed silver salts, said amount being within the range from 8 cos.to 30 grams per liter of solution, and a color-forming compound.

3. An aqueous photographic reducing bath containing as the sole type ofreducing agent at least one primary aromatic amino color developingagent, an aliphatic amine of 1-6 carbon atoms which is free fromnegative groups and hydroxyl groups attached to carbon in an amountsufficient to change the characteristics of the solution so that it nolonger distinguishes between exposed and unexposed silver salts, saidamount being within the range from 8 cc. to 30 grams per liter ofsolution, and a color forming compound.

4. An aqueous photographic reducing bath containing as the sole type ofreducing agent an betadimethylaminoethylamlne in an amount sui-,

ficient to change the characteristics of the solui tion so that it nolonger distinguishes between exposed and unexposed silver salts, saidamount being within the range from 8 cc. to 30 grams per liter ofsolution, and a color forming compound.

' EMERY MESCH'I'ER.

CERTIFICATE OF CORRECTION. Patent No. 2,510,980; February 16, 19M.

' EMERY- rmscnm.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page )4,second column, 1111618, for the patent number "1,155,957 read--2,155,957--;

and line 55, for "their" read --them-; and that the said Letters PatentShould be read with this correction therein that the same may conform tothe record of the casein the Patent Office.

. Signed and sealed thie 20th day of April, A. D. 1915.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,510,9 0; February 15, .1915.

EMERY HESCHTER.

It is hereby certified that error appears in the printed specificationof the abowie numbered patent requiring correction as follows: Page 11.,second columnfline 18, for the patent number "1,155,937" read"2,153,957";

and line 55, for "their" read --them--; and that the said Letters Patentshould be read with this correction therein that the "same may conformto the record '01 the ca e in the Patent Office.

Signed and sealed this 20th day of April, A. n. 1915. 7

Henry Van Aradale, (Seal) Acting Commissioner of Patents.

